Field of the Invention
The present invention relates to a disc drive having at least the function of playing back an optical disc or the like, and more particularly to a disc drive having a disc tray which transfers an optical disc such as a CD-ROM between a disc placing/removing position (eject position) and a playback position (loaded position), and a driving method of a loading motor in the disc drive.
Description of the Prior Art
One example of disc drives for playing back an optical disc such as a CD-ROM or the like is disclosed in Japanese Patent Application No. HEI 7-201605. FIG. 1 is an exploded perspective view which shows the structure of the disc drive of this application and FIG. 2 is a top plan view of the disc drive.
As shown in these drawings, the disc drive 1B is constructed from a main body 2 and a disc tray 5 which moves backwards and forwards with respect to the main body 2 so as to be insertable into and ejectable out of the main body 2.
The main body 2 of the disc drive is roughly constructed from a bottom plate 11, a main circuit board assembly 12 provided above the bottom plate 11, a mechanism assembly 13 provided above the main circuit board assembly 12, and a casing 14 enclosing the upper side of the mechanism assembly 13.
The casing 14 has a top plate 14a, and a disc clamper 38 is installed on the underside surface (inner surface) thereof so as to be rotatable coaxially with a turntable 26 which will be described later. The casing 14 is attached to the upper portion of the mechanism assembly 13 with screws 17. The bottom plate 11 is attached to the lower portion of the mechanism assembly 13 with screws 17 with the main circuit board assembly 12 being interposed therebetween.
In a front plate 14e of the casing 14, an aperture 14f is formed to allow the disc tray 5 to be passed therethrough. A front panel 15 having a similar aperture 15a is attached to the front plate 14e via a cushioning frame 16 made of sponge. An eject switch 18 for driving the disc tray 5 is provided on the front panel 15.
The mechanism assembly 13 includes a roughly container-shaped chassis 20 which is provided with a mechanism unit 22 and a loading mechanism 30. The mechanism unit 22 is arranged within a concave portion 21 formed in the bottom portion 20a of the chassis 20, and the loading mechanism 30 is arranged in a space defined in front of the concave portion 21.
The mechanism unit 22 includes a base 23 which is provided with a spindle motor 25 for rotating an optical disc, a turntable 26, an optical pick-up (optical head) 27, and an optical pick-up moving mechanism 28.
Further, a rear end portion (back side of the main body 2) of the base 23 is supported by an insulator 29a made of an elastic material such as a rubber. This enables the base 23 to be freely pivotal with respect to the chassis 20 about the mounting position of the insulator 29a.
The loading mechanism 30 is provided for displacing the mechanism unit 22 between a lowered position and a raised position with respect to the pivotal point by the insulator 29, as well as for moving the disc tray 5 between the eject position (disc placing/removing position) and the loaded position (disc playing back position). The loading mechanism 30 is roughly constructed from a motor 31 provided at a front portion of the chassis 20, a rotational speed reduction mechanism 32 for reducing the rotational speed of the motor 31, a cam wheel (ascending/descending gear) 33 which is rotated via the rotational speed reduction mechanism 32, and a base ascending/descending member 35 which is displaced (pivoted) in accordance with the rotation of the cam wheel 33.
The loading motor 31 for the disc tray 5 is a DC motor, and is driven at a specified speed by a constant voltage.
The rotational speed reduction mechanism 32 is constructed from a roller 32a of almost truncated cone shape fixed at the tip of the rotation shaft of the loading motor 31, a wheel 32b having on its top a bevel rubber sheet which is brought into close contact with the outer peripheral cone surface of the roller 32a, a large gear 32c which meshes with a pinion gear (not shown in the drawings) provided below the wheel 32b, and a small gear 32d fixed coaxially above the large gear 32c.
As shown in FIG. 3, the cam wheel 33 is formed of a plastic material, and it includes a lower gear 33a which meshes with the small gear 32d of the rotational speed reduction mechanism 32, and an upper gear 33b which meshes with a rack gear (not shown in the drawing) formed on the underside surface of the disc tray 5 along its longitudinal direction (in the forward and backward direction thereof). Further, a circumferential cam groove 34 is formed in the outer circumference of the axle portion between the gears 33a, 33b. The cam groove 34 consists of a lower cam groove 34a formed between the lower gear 33a and a flange 331 which is provided between the two gears 33a and 33b, an upper cam groove 34b formed between the upper gear 33b and the flange 331, and an inclined cam groove 34c which connects both cam grooves 34a and 34b. In this case, the upper cam groove 34b is formed over nearly the entire circumference of the cam wheel 33, and the lower cam groove 34a is formed over the center angle range of about 10-45 degrees of the cam wheel 33.
On the other hand, the base ascending/descending member 35 is located between the cam wheel 33 and the base 23 as shown in FIG. 2. The base ascending/descending member 35 has a pair of arms 35a and 35b arranged substantially in parallel, a connection portion 35c connecting both ends of the arms, and shafts 35d and 35e formed projecting from the respective ends of the arms. The member 35 is supported so as to be rotatable around the shafts 35d and 35e which are attached to the chassis 20.
Further, a projected follower 36 which engages with the cam groove 34 of the cam wheel 33 is provided so as to project from the base ascending/descending member 35 on the side opposite to the extension of the arms 35a and 35b. In the state in which the follower 36 is engaging with the upper cam groove 34b, the arms 35a and 35b are at a position rotated downward with the shafts 35d and 35e as the rotation axis. On the other hand, when the follower 36 is brought into engagement with the lower cam groove 34a via the inclined cam groove 34c according to the rotation of the cam wheel 33, the arms 35a and 35b move to a position rotated upward with the shafts 35d and 35e as the rotation axis.
The arms 35a and 35b of the base ascending/descending member 35 constructed as in the above are connected respectively to insulators 29b and 29c fitted to connection portions formed on both sides of the front portion of the base 23. Because of this, the front portion of the base 23 (mechanism unit 22) moves vertically between the raised position and the lowered position with the location of an insulator 29a situated on the back side of the main body 2 as the pivotal point in accordance with the pivotal movement of the arms 35a and 35b of the base ascending/descending member 35 which is caused by the rotation of the cam wheel 33.
The disc tray 5 includes a shallow concave disc supporting portion 5a for supporting an optical disc 3 (hereinafter, simply referred to as "disc" on occasion) thereon, and the rack gear is formed on the underside surface thereof (not shown in the drawing) such that it meshes with the upper gear 33b of the cam wheel 33. Consequently, as the cam wheel 33 is rotated by the rotation of the loading motor 31, the disk tray 5 is moved forward or backward with respect to the main body 2 between the disc unloading position (eject position) and the disc loaded position (playback position). In this case, as stated in the above, since the loading motor 31 is constructed so as to rotate in a constant speed with a constant voltage, the disc tray 5 also moves in a constant speed.
When the disc drive 1B is not in use, the disc tray 5 is housed within the main body 2 (at the disk loaded position). In this state, if an eject operation (unloading operation) is carried out, the motor 31 rotates in a prescribed direction, and the rotation of the motor 31 is transmitted to the cam wheel 33 with a reduced speed, whereby the cam wheel 33 is rotated in a counterclockwise direction in FIG. 1. This rotation of the cam wheel 33 causes the disc tray 5 to move forward and protrude to a position (the disc eject position) outside the main body 2 through the apertures 14f, 15a.
In this state, a disc 3 is placed in the disc supporting portion 5a of the disc tray 5, and a loading operation is then carried out, whereby the loading motor 31 rotates in the opposite direction, and this causes the cam wheel 33 to rotate in the opposite direction (anti clockwise direction in FIG. 1) via the rotational speed reduction mechanism 32. Consequently, the disc tray 5 is moved toward the back of the disc drive into the main body 2, through the apertures 14f, 15a, to the disc loaded position. In this way, the optical disc 3 which is placed at a prescribed position on the disc tray 5 is also transported to the disc loaded position in the main body 2.
Now, the following two operations are known as the loading operation of the disc. Namely, the first is the eject switch loading operation in which the eject switch 18 is turned on to rotate the loading motor 31 in the reverse direction so that the disc tray 5 is moved automatically to the disc loaded position. The second is the manual loading operation in which a switch 37 installed within the cam wheel 33 is operated by manually pushing the disc tray 5 to a specified position in the direction of an arrow A in FIG. 1. With this operation, the loading motor 31 is driven and thereafter the disc tray 5 is moved (loaded) automatically to the disc loaded position.
In the manual loading operation, when the disc tray 5 is pushed in manually, the cam wheel 33 has to be rotated forcibly because the rack of the disc tray 5 is in engagement with the cam wheel 33. Since the cam wheel 33 is connected to the loading motor 31 via the rotational speed reduction mechanism 32, the gears and the like of the rotational speed reduction mechanism 32 and the loading motor 31 have also to be rotated. Because of this, if the gear ratios of various gears of the cam wheel 33 and the rotational speed reduction mechanism 32 are high and therefore the rotational speed reduction ratios are also high, the force required for the manual operation becomes large.
Further, when the cam wheel 33 begins to rotate in the opposite direction, the follower 36 of the base ascending/descending member 35 relatively moves along the upper cam groove 34b and the center of the disc 3 approaches the central hub portion of the turntable 26, the follower 36 is displaced into the lower cam groove 34a so that the follower 36 is shifted downward, thereby the base ascending/descending member 35 is rotated around the axes 35d, 35e so that the arms 35a, 35b are displaced from the lower position to the upper position.
According to the displacement of the arms 35a, 35b, the front portion of the base 23 pivots about the position of the insulator 29a from the lowered position to the raised position through the insulators 29b, 29c, whereby the base 23 is placed in a roughly horizontal state.
In this way, the center portion 26a (center hub portion) of the turntable 26 is fitted into a center hole 3a of the optical disc 3 to support the optical disc 3 thereon, and at this time the disc clamp 38 is magnetically stuck to the turntable 26, thereby the optical disc 3 is held between the turntable 26 and the disc clamp 38. In this state, the spindle motor 25 is operated to rotate the optical disc 3 at a predetermined rotational speed, and then the information recorded on the optical disc is played back. If an eject operation is carried out while the rotation of the optical disc 3 is stopped, the operations of each mechanism of the disc drive 1B described above are carried out in reverse order and direction, thereby the clamp is released and then the optical disc 3 supported on the disc tray 5 is ejected.
As described in the above, in the disc drive 1B, the loading and ejecting operations of the optical disc 3 are carried out by moving the disc tray 5, in which the loading motor 31 is employed as a driving means. However, when the rotation of the optical disc 3 is interrupted by the halt of operation of various parts of the disc drive such as the motors because of the power failure or the like, in particular, when the power failure occurs during playing back the optical disc 3, it becomes not possible to eject the optical disc 3 by moving the disc tray 5. In order to avoid such a situation, there is provided an emergency eject mechanism 38 which makes it possible to manually move the disc tray 5 to eject the optical disc 3.
The emergency eject mechanism 38 is provided on the cam wheel 33. Describing it in more detail, as shown in FIG. 2 and FIG. 3, a plurality (three in this embodiment) of engaging pieces (projections) 38a, 38b, and 38c are provided in the peripheral space of the cam wheel 33 between the flange 331 and the lower gear 33a. Each of these pieces 38a, 38b, and 38c constitutes an engaging portion with which the tip of a rod-like slender operating member 39 can engage for the purpose of manually operating the cam wheel 33 to rotate it from the outside of the main body 2.
Here, if a power failure, for example, occurred during playback of the optical disc 3 and the disc tray 5 is stopped at the disc loaded position (inner-most portion) or its neighborhood, a pin 39a of the operating member 39 is inserted through the hole 15c of the front panel 15 into the inside of the main body 2 to cause its tip to be engaged with the engaging piece 38a, as shown in FIG. 2 and FIG. 3, and then the engaging piece 38a is manually pushed by the pin 39a in the direction of an arrow B in FIG. 2. As a result, the cam wheel 33 is rotated counterclockwise in FIG. 1 to cause the mechanism unit 22 move downward (that is a position where the disc tray 5 can be moved), and thereby disc tray 5 is slightly moved forward. In this case, the motor 31 is also forcibly rotated via the rotational speed reduction mechanism 32 in accordance with the rotation of the cam wheel 33. As described above, since the operation of the emergency eject mechanism is carried out by forcibly rotating the cam wheel by inserting the operating member from the outside of the disc drive, the burden on the manual operation is heavy when the gear ratio of the loading mechanism 30 is high.
As the cam wheel 33 is rotated to a certain extent, the front end portion of the disc tray 5 protrudes out of the aperture 15a, so the disc tray 5 can forcibly be moved to the eject position by gripping the projected portion with a hand and pulling it out forward. In this way, it becomes possible to take out the optical disc 3 placed on the disc tray 5.
In the prior art disc drive 1B with the above construction and operation, the moving speed of the disc tray 5 is determined by the rotational speed reduction ratio of the cam wheel 33 of the loading mechanism 30 and the rotational speed reduction mechanism 32 provided that the rotation of the loading motor 31 is constant. Here, what is meant by the "rotational speed reduction ratio" is the ratio of the number of rotations of the output on the driven side in a specified time to the number of rotations of the input on the driving side. In the case of this prior art disc drive, when the roller 32a fitted to the rotation shaft of the motor 31 and the wheel 32b are regarded as being some sorts of gears, the rotational speed reduction ratio means the ratio of the number of rotations of the cam wheel 33 to the number of rotations of the roller 32a within a specified time. In such a rotational speed reduction mechanism, the gear ratio of a pinion gear (not shown in the drawings) provided below the wheel 32b with respect to the large gear 32c and the gear ratio of the small gear 32d to the gear 33a below the cam wheel 33 are related to the speed reduction ratio. Therefore, when these gear ratios are high, the rotation of the motor 31 on the drive side is transmitted to the cam wheel 33 on the driven side with more reduction in the speed.
In the loading mechanism 30 of the prior art disc drive, there is a relation such that the moving speed of the disc tray 5 is decreased as the gear ratio of the loading mechanism is raised, and the moving speed of the disc tray 5 is increased as the gear ratio is lowered. In this case, if the moving speed of the disc tray 5 is too fast, it will give rise to various problems that will be described in detail later. Accordingly, in the prior art disc drives, the gear ratios are set at relatively high values to suppress the moving speed of the disc tray 5 at a relatively slow speed.
In this way, the gear ratios of the loading mechanism 30 are set at relatively high values in the prior art disc drives. Accordingly, the emergency eject operation in which the disc tray 5 is forcibly moved manually to the eject position by the use of the emergency eject mechanism 38, or the manual loading operation in which the disc tray 5 is pushed in manually to the specified position in the manual loading operation requires a large force to carry it out, which results in a problem in that the operability of thereof.
In other words, in the emergency eject operation, the slender pin 39a of the operating member 39 is inserted from the outside of the main body 2 of the disc drive 2 to directly and manually rotate the cam wheel 33, by which the various gears of the rotational speed reduction mechanism as well as the loading motor 31 are forcibly rotated. Accordingly, if the gear ratio of the rotational speed reduction mechanism 30 is high, the operation requires a large force. As a result, it leads to the problem that not only the emergency eject operation becomes less easy to carry out but also unreasonable loads are placed on the operating member 39, the cam wheel 33, and the like. In addition, in the emergency eject operation, the disc tray slightly stuck out of the main body 2 is forcibly withdrawn, in which case a large force is required also.
Moreover, in the manual loading operation, when the disc tray 5 is pushed in manually, the cam wheel 33, various gears of the rotational speed reduction mechanism 32 and the loading motor 31 are forcibly rotated also via the rack of the disc tray 5. Consequently, if the gear ratios of the loading mechanism 30 are high, the manual loading operation becomes less easily feasible, and the force required for pushing in the disc tray 5 becomes large accordingly. As a result, an excessive force might be applied to the disc tray 5, thereby placing an unreasonable load on the loading mechanism 30.
These problems can be resolved by reducing the gear ratios of the loading mechanism 30. However, if the gear ratios of the loading mechanism 30 are reduced, the moving speed of the disc tray 5 becomes fast on the contrary, which gives rise to the problem of the durability of the disc 3 and the loading mechanism 30 because of the excessive load on them. Namely, since the moving speed of the disc tray 5 is held at a constant level during the loading operation owing to the fact that the loading motor 31 is driven at a specified number of rotations by the constant voltage of the loading motor 31, if the moving speed of the disc tray 5 is fast, heavy loads are imposed momentarily on the disc 3 and the loading mechanism 30 when the disc tray 5 is stopped.
Accordingly, in the prior art disc drives, the gear ratio of the loading mechanism 30 is designed to be relatively high such that the speed reduction ratio is high in spite of the drawback that a large force is required for the emergency eject operation and the manual loading operation.